This invention relates to air conditioning apparatus. In particular, the invention is directed to air conditioning apparatus, especially for the cabin of a vehicle, in which the apparatus includes: a first circuit branch for the flow of a refrigerant fluid therein, the first circuit branch containing a compressor which is arranged to receive the refrigerant fluid in the gaseous state and to compress it to a supercritical pressure, and a second circuit branch containing a first heat exchanger which is adapted to cool the fluid compressed by the compressor at a substantially constant pressure, by transferring heat from a first external medium to the fluid; a first expansion device which is adapted to reduce the pressure in the fluid leaving the first heat exchanger, so as to put at least some of the fluid in the liquid state; and an evaporator which is arranged to change the state of the fluid received from the first expansion device from the gaseous to the liquid state at a substantially constant pressure, by taking heat from a second external medium for the purpose of cooling the space (for example the cabin of a vehicle) which is to be air conditioned. The fluid thus vaporised is then aspirated by the compressor.
Forms of apparatus of the above general type are described for example in the specifications of International Patent Publication No. WO93/06423, U.S. Pat. Nos. 5,245,836 and U.S. Pat. No. 5,291,941. The refrigerant fluid used in these apparatuses is typically carbon dioxide (CO2).
Where it is not required to cool the air which is to be delivered into the cabin of a vehicle, but merely to heat it, it is usual to make use of the heat which is produced by the propulsion engine of the vehicle, for example by passing air in contact with a heating radiator through which the engine coolant fluid flows. When the engine is cold, no heat can be drawn from it for the purpose of heating the cabin. This results in a considerable delay before the cabin can be brought to the required temperature, and is consequently detrimental to the comfort of the occupants of the vehicle. In some cases, the coolant liquid never, during the whole duration of a journey, reaches a high enough temperature to warm the occupants as they would wish.
In order to enable the cabin to be brought to the required temperature more quickly, various supplementary devices may be used, in particular those which involve the use of heaters or electrical radiators, but these are somewhat expensive.
An object of the present invention is to enable a space, for example the cabin of a vehicle, to be heated more rapidly than hitherto when the engine is cold, or to top up the quantity of heat where the heat available is insufficient, without the need to provide any costly specific means for this purpose.
According to the invention, an air conditioning apparatus, especially for the cabin of a vehicle, including for the flow of a refrigerant fluid therein, comprises a circuit having: a first circuit branch which contains a compressor adapted to receive the said fluid in the gaseous state and to compress it to a supercritical pressure, and a second circuit branch containing a first heat exchanger arranged to cool the fluid compressed by the compressor at a substantially constant pressure, by transferring heat to a first external medium; a first expansion device adapted to reduce the pressure of the fluid leaving the first heat exchanger so as to put at least some of this fluid into the liquid state; and an evaporator to put into the gaseous state the fluid derived in the liquid state from the first expansion device, at a substantially constant pressure by taking heat from a second external medium for cooling the space to be air conditioned, with the fluid thus vaporised being subsequently aspirated by the compressor, is characterised in that the circuit further includes a third branch which is disposed in parallel with the second branch and which contains a second expansion device and a second heat exchanger, for transferring heat from the refrigerant fluid to the said second external medium so as to heat the said space, means being provided for causing the fluid to flow selectively in an air conditioning loop constituted by the said first and second branches, or in a heating loop constituted by the said first and third branches.
The second expansion device may be disposed either upstream or downstream of the second heat exchanger.
A first pressure sensor is preferably disposed in the first branch, downstream of the compressor.
A second pressure sensor is preferably disposed in the second branch, between the first heat exchanger and the first expansion device.
A non-return valve is preferably disposed in the second branch, downstream of the evaporator.
According to a preferred feature of the invention, the circuit includes at least one internal heat exchanger which is adapted to transfer heat between one section of the first branch, situated downstream of the compressor, and either a section of the second branch situated between the first heat exchanger and the first expansion device, or a section of the third branch which is situated upstream of the second heat exchanger.
In some embodiments of the invention, the above mentioned sections of the first, second and third branches may contain, respectively, the three heat exchanger elements of a three-way internal heat exchanger.
In other embodiments, the said sections of the first and second branches contain respectively the two ways, or heat exchanger elements, of a two-way internal heat exchanger, while the said sections of the first and third branches contain respectively the two ways, or heat exchanger elements, of a two-way second internal heat exchanger.
The said section of the third branch may be situated either downstream or upstream of the second expansion device.
A third expansion device is preferably disposed in the third branch upstream of the said section of the third branch.
The said section of the second branch is situated upstream of the second pressure sensor, where the latter is provided.
The said second external medium is preferably a stream of air which is then passed into the space such as the cabin of the vehicle.
The evaporator and the second heat exchanger are disposed in series, in that order, in the path of the said stream of air in preferred arrangements.
A heat source external to the refrigerant fluid circuit is preferably disposed in the path of the said stream of air. It may be disposed in this path downstream of the second heat exchanger, or between the evaporator and the second heat exchanger.
Means are preferably provided for varying the thermal power transmitted from the second heat exchanger to the said second external medium. These power varying means may comprise means for adjusting the second expansion device and/or the third expansion device. They may, alternatively or in addition, comprise means for adjusting the capacity or speed of the compressor.
Preferably, a reservoir is disposed in the air conditioning circuit upstream of the compressor.
The various features and advantages of the invention will appear more clearly on a reading of the following detailed description of some preferred embodiments of the invention, which are given by way of non-limiting example only and with reference to the accompanying drawings, in which those elements which are identical or similar to each other are designated in all the Figures by the same reference numerals.